Gold/silver alloys

ABSTRACT

A tarnish resistant Au/Ag alloy of low gold content exhibiting properties desired in jewelry manufacture consisting essentially of about 25 to 30 percent, by weight, gold, about 45 to 57 percent, by weight, silver, about 18 to 25 percent, by weight, of a metal selected from the group consisting of copper, nickel and mixtures thereof and 0 to about 5 percent by weight zinc.

United States Patent 1191 Kohrn et al. 5] Dec. 9, 1975 GOLD/SILVER ALLOYS 3,767,391 /1973 Tuccillo et a] 75/134 c [76] Inventors: Edward Louis Kohrn, 9 Sunset FOREIGN PATENTS OR APPLICATIONS Drive. Cap Ar h rna Park, 746,755 6/1933 France 75/134 c M 21146; Seymour Globus, 268 87!,747 5/1942 France 75/173 R Wakely Terrace, Bel Air, Md. 622,474 [1/1935 Germany 75/173 C 21014 652,45] lO/l937 Germany 75/173 R 654.357 12 I937 G 1.75173 C 22 Filed: June 19, 1974 [2|] Appl. No.: 480,890 Primary ExaminerC. Lovell Assistant Examiner-E. L. Weise us- CL IIIIIIIII u 75/134 C; 5/64 F; 75/173 R; Attorney, Agent, or Firm-Larson, Taylor and Hinds 75/173 C 51 11.1.0. c22c 5/06 {57] ABSIRACT 5 Field f Search 75/173 R, 173 C 134 C A tarnish resistant Au/Ag alloy of low gold content ex- 75 34 F 5 hibiting properties desired in jewelry manufacture consisting essentially of about to percent, by [56] References Cited weight, gold, about to 57 percent, by weight, silver, UNITED STATES PATENTS about 18 to 25 percent, by weight, of a rnetal selected from the group consisting of copper, nickel and mix- 1,090,939 3/1914 Newton /!73 C tures thereof and 0 to about 5 percent by weight Zinc 2,2l6,495 l0/l940 Loeblch 3,424,577 H1969 Nielsen et a1. 75/134 (3 5 Cl ims, No Drawings GOLD/SILVER ALLOYS BACKGROUND OF THE INVENTION This invention relates to improvements in gold base alloys. More particularly the present invention is directed to low gold alloys possessing the properties desired in the manufacture of articles of jewelry.

Gold, per se, being a relatively solt metal is unsuitable for the manufacture of jewelry articles and must be alloyed with other metals so as to acquire the properties that make it serviceable for jewelry purposes. The most desirable properties for jewelry purposes in gold base alloys are castability, workability, tarnish resistance, luster and color. To achieve these properties it is generally necessary for the gold content of the alloys to be at least 41 .65% by weight (i.e., at least 10 karat). It is well recognized that gold base alloys containing levels of gold lower than about 41.65% exhibit low tarnish resistance and quite often poor castability and workability. These drawbacks which characterize low gold alloys are particularly true of the gold/silver alloys of the prior art.

Attempts have been made to overcome this problem of poor tarnish resistance in below 10 karat gold/silver alloys by the inclusion in such alloys of minor amounts of other metals. Unfortunately these efforts have not been without their shortcomings for while tarnish resistance may be improved by such additions, one or more of the other desired properties, i.e. workability, castability including porosity, luster and color are invariably adversely effected.

OBJECTS OF THE INVENTION One object of the present invention therefore is to provide a low gold alloy which possesses all the desired properties for jewelry manufacture.

Thus, it is an object of the invention to provide a low gold base alloy that can be worked, cast, molded, engraved, soldered and stamped using existing techniques with normal jewelry equipment.

It is also an object of the invention to provide a low gold alloy which is of sufficient hardness to take a normal jewelry finish either bright or textured as desired.

Yet another object of the invention is to provide a low gold base alloy of excellent color and luster.

A further object of the invention is to provide a low base alloy which in addition to possessing the aforementioned properties manifests a high tarnish resistance under normal usage.

Lastly, it is an object of the invention to provide at substantially reduced cost a low gold alloy which is a substitute for and which possesses all the beneficial properties of 10-14 karat gold base alloys.

SUMMARY OF THE INVENTION These and other objects of the invention are obtained by a metal alloy consisting essentially of about 25 to 30 percent, preferably 27 to 29 percent, by weight, gold; about 45 to 57 percent, preferably 47 to 55 percent, by weight, silver; about 18 to 25 percent, preferably about l8 to 23 percent by weight of a metal selected from the group consisting of copper, nickel and mixtures thereof and to about percent, preferably about 1 to 3.5 percent by weight zinc.

DETAILED DESCRIPTION The color of the alloys of the invention are either yellow or white depending upon whether or not nickel is present. In the absence of nickel the color of the alloy is yellow and in the presence of nickel the color of the alloy is white. When nickel is employed and a white alloy is desired the weight ratio of copper to nickel is about 2 to 3:1.

Illustrative of preferred yellow alloys are those consisting essentially of about 25 to 30 percent by weight, gold, about 45 to 57 percent by weight, silver, about 18 to 20 percent by weight, copper and about 1 to 3.5 percent by weight, zinc.

Preferred white alloys consist essentially of about 25 to 30 percent by weight, gold, about 45 to 47 percent by weight, silver, about 18 to 25 percent by weight of a mixture of copper and nickel wherein the weight ratio of copper to nickel is about 2 to 3:1 and about 2 to 3 percent by weight zinc.

The process of manufacturing the alloys of the invention does not differ from the standard practice in the manufacture of alloys of precious metals. The alloys may be prepared by simply weighing out the proper proportions of the constituents, placing them in a refractory crucible and subjecting the mixture to a heat sufficient to melt the materials. Care should be taken, however, to insure uniform alloying and mixing of the constituents.

A more convenient method for preparing alloys of the invention comprises alloying in equal proportions either 14 karat yellow gold or l4 karat white gold with sterling silver. The composition of 14 karat yellow gold generally is as follows: 56.25% Au, 30.732.8% Cu, 4.2l0.5% Ag and 2-7% Zn. l4 karat white gold on the other hand is ordinarily composed of 56.25% Au, 24.6% Cu, 12.8% Ni and 5.0% Zn. Sterling silver is constituted of 92.5% Ag and 7.5% Cu. Thus, the con stituencies of these materials is such that 50/50 blends of either the white or yellow 14 karat gold and sterling silver provides novel low gold alloys of the invention.

The following example is included to further illustrate the present invention.

EXAMPLE A 50/50'blend of 14 karat yellow gold and sterling silver were weighed and charged together into a refractory crucible wherein they were heated to a temperature of l600F with a gas torch until completely melted. The melt was stirred with a graphite rod immediately prior to casting and the alloy melt was then cast in air into a standard investment mold in the form of a ring. Upon cooling the alloy casting was removed and found to be sound with good surface fidelity and without unsightly porosity.

The head of the ring was subsequently mechanically worked, chased and burnished. All of these operations were completed with the same ease and pleasant results that are obtained with 10-14 karat gold alloys.

The finished ring was worn continuously for three months in a city environment without tarnish and without loss of form, color, luster, or polish.

A similar article of jewelry is obtained possessing like properties by substituting 14 karat white gold for the l4 karat yellow gold.

While the features of this invention have been disclosed with reference to the specific embodiments described therein, it is to be understood that various modweight, silver, about [8 to 25 percent, by weight, of copper.

3. A metal alloy consisting essentially of about 25 to 30 percent, by weight, gold, about 45 to 57 percent, by weight, silver, about 18 to 20 percent by weight copper and about 1 to 3.5 percent, by weight, zinc.

4. An article ofjewelry formed of the alloy of claim 1.

S. An article ofjewelry formed of the alloy of claim 3. 

1. A METAL ALLOY CONSISTING ESSENTIALLY OF ABOUT 25 TO 30 PERCENT, BY WEIGHT, GOLD, ABOUT 45 TO 57 PERCENT, BY WEIGHT, SILVER, ABOUT 18 TO 25 PERCENT, BY WEIGHT, OF COPPER AND 0 TO ABOUT 5 PERCENT BY WEIGHT ZINC.
 2. A metal alloy consisting essentially of about 25 to 30 percent, by weight, gold, about 45 to 57 percent, by weight, silver, about 18 to 25 percent, by weight, of copper.
 3. A metal alloy consisting essentially of about 25 to 30 percent, by weight, gold, about 45 to 57 percent, by weight, silver, about 18 to 20 percent by weight copper and about 1 to 3.5 percent, by weight, zinc.
 4. An article of jewelry formed of the alloy of claim
 1. 5. An article of jewelry formed of the alloy of claim
 3. 